Geological testing method



Patented Sept. 14, 1926.

UNITE GEOLOGICAL TESTING IiIETHOD.

Application filed December 13, 1920, Serial No. 430,432, and in GermanyDecember (GRANTED UNDER THE raovrsrous or THE ACT or MARCH s, 1521, 41STAT. a, 1313'.)

My invention relates to a method of ascertaining the geologicalstructure of the strata appertaining to a particular region such methodbeing useful in particular for mining operations when developing a lodeor opening a seam. Up till now in all those cases where the naturalformation of the ground does not throw light upon the subject, recoursemust be had to borings. However, the sinking of bore holes regularlyconstitutes a tedious and expensive operation which moreover cannot evenbe em- I ployed in all cases. Again, whenever it has been merely aquestion of primarily obtaining an idea of the approximate compositionof the strata, the divining-rod has been, as may be well known,experimented with. Notwithstanding, as is well known to those skilled inthe art, it has been so far impossible to establish an indisputableconnection between the action of the divining rod and the geologicalpeculiarities of the subsoil. -A second. method of working and servingthe same end of securing merely approxi- 525' mate data, consists in theapplication of electric waves from the action of which certain definiteinferences are then drawn'as to the arrangement and the peculiar natureof the strata. 80 Now in accordance with my invention it is likewiseintended that waves per se shall be employed for the purpose ofascertain ng the arrangement of the strata, however, not electric wavesbut elastic waves, produced by mechanical means. I employ these waves inappreciation of the fact that the connection of such mechanicallygenerated waves with the properties of the strata, such as density andelasticity, will be far more direct and therewith far more intimate thanthe correlation to electric waves. To this end, there-are generated inaccordance with my invention within the measuring area and at a suitablepoint thereof, artificial mechanical waves, say, for instance, by thedetonation of a certain quantity of explosives, the

elastic propagation of these mechanical waves through the different bedsbeing recorded by a seismograph set up at a suitable distance remotetherefrom. The records thus obtained are then made use of in exactly thesame manner customary in Seismology rious depths. I am aware that inseismolo attempts have already been made to arrive at certainconclusions relativel eral geological formation of t e whole.

For general information on this comparatively recent art reference ismade, especially with regard to the use of traveling time curves orsometimes shortly called time curves, to Modern Seismology by G. W.Walker, published in 1913 by Longmans, Green & Company, New York andLondon, whereon page 53 and following, the function and use oftraveling, time curves in Seismology is dealt with in detail. For thepresent purposes the use of these curves will be shortly explainedhereinafter.

Thus far, however, the investigators were to the genearth as a able bysuch observations to only draw approximate and general conclusions as tothe structure of the entire earth, and at that with observations basedonly on accidental natural earth shocks of uncontrollable duration andorigin. d

On the other hand, in the present instance, so the noteworthy feature isthat the observations to be effected does not rely upon the uncertainoccurrence of natural earthquakes, but that there are produced,purposely and by special means, artificial earth shocks, in consequenceof which alone the possibility is created of carrying out observationsof this character for a particular locality and for a definite period oftime. Of essential importance in this connection is moreover the factthat by means of my improved method there is now also provided aconvenient form of'comparative measurement for the purpose ofdetermining the propagation of the elastic waves within the strata andof their time of arrival at the seismometer, respectively, by employing,for f the purpose of ascertaining the moment when the elasticoscillations are excited, either the sound waves created in any case onthe detonation of the explosive charge, or else by effecting atransmission by means of light, electric current or electric waves,-respectively. I

ioly

From the surface speed and the three di-.

mensio'nal speed of the waves, as also from the depths down to which thewaves have penetrated the strata, but in particular, from the mutualrelation of the velocitiesof the longitudinal and transversal waves,inferences may be drawn respecting the elastic properties of the stratatraversed by the waves..- It-will thus be found that especial from thepoints of inflection and the bends in the travelling time curve, theremayialwa s be inferred that there exist fissures in t e elasticproperties of the strata, as also inflections, refractions,andreflections at the marginal levels thereof.

The manner in which my novel method is employed is illustrated in theaccompanying dia ams in which:

lgure 1 diagrammatically represents the I artificially produced earthshock and its 'a ammatica traveling time has been recorded;

Figure 3 is a straight line traveling time curve composed from aplurality of inclividual observations such as are recorded on the tapeshown in Figure 2;

Figure 4 represents a straight line velocity curve resulting from thetraveling time curve in Figure 3;

Figure 5 represents a bent traveling time curve as a resultant ofincreasing density of the ound under observation;

Figure 6 re resents a velocity and a depth curve obtaine from thetraveling time curve in Figure 5; V

Fi re 7 represents diagrammatically a trave in time curve with ends init as a result- 0 .a sudden change in the character of the underlyingstrata; and

Figure 8 represents the velocity and depth curves obtained from theplotged in the traveling time curve Figure Referring to Figure 1, 1represents a recording field seismograph for the purposes of the presentinvention and of a construction and character described and illustratedin my U. S. Patent No. 1,451,080, dated April 10th, 1923. The recordingseismograph shown in Figure f that patent consists of a pendulum deviceand a photographic recorder, both of which instrumentalities may beassumed to cooperate in the present case as described in theaforementioned patent, the pendulum device being denoted in the presentFigure 1 with 2 and the photogra h1c recording device being dillindicated at 3. At a suita le distance rom the seismograph 1 a cartridge4 filled with suitable explosives is located and an electric circuit 6is established between the cartridge and the re observations cordingdevice 3, including the battery 5, of such character that when thecartridge is exploded the circuit is interrupted and thus, by suitablemeans described in the aforementioned patent, a mark 9 is made on therecording tape illustrated inf'present Figure 2.

Referring to Figure 2 a tape portion is shown at 7 and assumed tocontinuously travel at a certain rate of speed, means being provided inthe recordiug apparatus to make recording marks at stated equal timeintervals, for instance in seconds, as shown at the lower tape edge inFigure 2. So long as no shocks arrive at the seismograph a strai htcentral line 8 is recorded on the tape y the means provided in theaforementioned apparatus. As soon as a shock disturbs the equilibrium ofthe seismograph pendulum, the mirror of the instrument oscillates andinstead of making a stralght line record on the tape, oscillations suchas are shown at a or b or c are recorded.

By other suitable means shown and described in aforementioned patent,the interruption of the circuit 6 on the ex losion of the cartridgerecords the vertica mark 9, above referred to, on the tape shown inpresent Figure 2. The time which has elapsed between the initial mark 9and the appearance of the first oscillation a is called the travelingtime of the. elastic wave. A number of separate subsequent waves oroscillations are generally recorded on the tape due to the sameexplosion or shock. The first oscillations a are due to the elasticwaves traveling through the ground, the

second oscillation b are air waves and. the third oscillations c areusually due to very long ground waves.

For the present explanation it is sufficient to receive .the firstsharply defined short ground waves noted by the oscillations a. Thetraveling time t thus recorded constitutes the time which these wavesconsumed in travelin from the point of origin to the seismograph.

This time will be the greater the further the seismograph is removedfrom the origin of the shock. Thus if the recording apparatus be assumedto remain stationary in one certain place and if successively a numberof cartrldges are explode-d along a straight line further away from theseismograph, but

at equal distances from each other, the traveling time increases inhomogeneous round proportionate tothese distances. uch a straight linetraveling time curve is shown in Figure 3 in which the ordinatesrepresent the traveling times t and the abscissae represent thedistances e from the seismograph, at which the shocks have beenproduced. In the example given the shocks are roduced at the distancese,, 6 e e,,, an accordingly the'values of the traveling times 13 speedsof velocities of the wave for; the different distances are obtained as:

Being assumed that:

fi=fi=fik 1 1 a a n It follows that:

In other words, the speed of the waves is constant, and therefore, thisexplains why the traveling time curve is a straightline. Thus in thegraph shown in Figure 4 in which the speed of the waves is plottedagainst the increasing distances e, the speed curve is a straight linein parallel to abscissaei line of the graph. Since the speed curve showsa constant speed, the corresponding depth curve would also show aconstant depth and would accordingly be represented as a straight linecoinciding with the abscissae line, which shows that the depth is zero.In other Words, this indicates that' the waves have traveled along thesurface of the ground in the example assumed in Figures 3 and 4.

In Figures 5 and 6 are illustrated graphs which more closely resembleactual observations, even though it is assumed in this ex ample, thatonly one strata is observed. The observations represented in Figure 5are again assumed to have been made with shocks produced at differentdistances 6,, 6 e from the point of observation. It will be noted,however, from the uniformly curved character of the traveling time curvethat the traveling time does not increase proportionately with-thedistance. In this graph the approximate paths of the elastic waves areindicated by lines provided with arrows, and it will be noted that thedeeper the shocks penetrate into the ground the shorter becomes theirtraveling time, i. e., the more their speed increases. The correspondingtraveling speed curve is shown in Figure 6. Such an increase in speedwith increase in distance between the point of shockorigin and the pointof observation would be caused for instance in sandy soil by the factthat quite naturally the sand is comparatively loose at and near thesurface, whereas it increases in density with the depth owing to theincreased pres sure of the upper layers of sand. Thus the curved pathsof the elastic waves shown in Figure '5 are produced, penetrating deeperand deeper into the ground as the distance is increased, whereas inFigure 4, which assumes theoretically uniformly loose-soil, the

shocks'would only travel along the surface 7 of the ground. It thusfollows that the traveling time curve will be curved the more, the morethe density of the sub-surface increases, in other Words, the more thetraveling speed of thewaves increases with the depth.

Inversely a definite increase in speed observed corresponds with adefinite increase in depth which the traveling waves have attained ontheir way from the point of origin to the point of observation. Figure 6illustrates the depth curve corresponding with the speed curve plottedfrom the observations. The different speeds observed at the differentdistances are easily calculated from the traveling time curve originallyobtained from the observations and shown in Figure 5 as follows:

In the examples represented by the combined graph and subsoil diagramFigure 7 and the graph Figure 8, the case is assumed that a strata ofconsiderable density, for lnstance lime stone, underlies a comparative-1y soft upper strata, for instance loose sand. When observations aremade in such a case the traveling speeds, instead of gradually anduniformly increasing with the. distance as shown in Figure 5, increaseabruptly from the point at which the elastic waves, heretofore travelingin loose sand, enter the dense lime stone. At such a point the travelingtime curve suddenly shows a sharp bend (at k in Figure 7). While thusthe speed derived from the first part of the curve shows the travelingspeed in the upper loose strata. the portion of the curve following thebend gives an indication of the propagation speed in the lower denserstrata. Such observations result then in a speed curve as shown inFigure 8 which shows a sudden increase in speed when the waves enter thedense-r strata, and correspondingly the depth curve assumes a suddendownward path at this point.

These simple examples given, plainly demonstrate that by thus observing011 the surface of the ground the varying speeds of the elastic waves inunderlying strata, the desired information as to the condition of thesubsoil may be ascertained without physically examining the differentstrata, such for instance as by bore holes. Such seismic observationsgive the very definite information that a certain depth a strata ofdifferent character underlies the strata directly ascertained from theobserved traveling time curve.

For example, referring to Figures 7 and 8, let a, and '0 representrespectively the speeds of the elastic waves in the upper and in thelower strata and let k be the distance of the bend in the traveling timecurve from the starting point of the traveling time curve (0), then thedepth H of the lower strata is calculated from the equation:

2 wherein 0 represents a function depending 1 v upon the relation andwhich is known the value of a would be calculated as 0.32 according towell known formulae. If new the point at which the traveling time curvebends is measured as 100 meters, the depth of the denser strata would be32 meters. k

For general information to those skilled in the art attention hasalready been called hereinbefore to; the book entitled ModernSeismalogy. by G. V. Walker, which contains all information necessar tomake the required calculations referre to hereinbefore, the presentmethod being a novel embodiment and novel practical use of the seismictheories earlier developed.

However, the factor a may in practice also be determined emperically byrecording traveling time curves in a territory which has beencompletely. explored as to its geological character by actual drilling oerations. Such emperical methods woul 'obviate making use of many of theformulae used in natural seismological observations and calculations. 1

Observations of the above mentioned character also enable theascertainin of the presence of a number of difierent layers of differentdensity. Inthe same manner as explained hereinbefore the character anddepth of the individual layers may be ascer' tained by observing thedilferent bends in the traveling time curve. V

Even though by these means it will not in all cases be always possibleto exactly determine the particular species of mineral per se, yet itwill in eneral suflice to ascertain to what depth t 1e strata visiblyappearing on the surface extend and what is the thickness of the moresolid or looser layers following thereunder, respectively, whether themanner in which the layers supceed each other corresponds to the normalgeological formation of the region or not. This point is of paramountimportance in -fillingin geological maps or when it becomes a questionof fixing the spots in a certain regionwhere bore-holes and shafts-areto be sunk. Then again, for instance, deposits of lignite and rock-saltevince such a characteristic elastic reaction that deposits of'thisnature may be directly ascertainedwhile making due use of otherobservationsby means of my improved method. At the same time, the saidimproved method itself is extraordinarily cheap and simple, since onl afew pounds of explosives are all'that 1s vrequired for each observation,while the seismometer employed in connection therewith is so constructed as to constitute a simple, light and handy instrument. Besides,the persons required to carry out the field operations need by no meanshe scientifically trained, as the computation of the results obtained bythe observations may be carried out along scientific lines subsequently.In this manner the sub-surface conditions of several square miles ofterritory may be ascertained in a few weeks, in other words, at anextremely small fraction of time and cost required forthe sinking of asingle bore hole. The

improved method may also'be made use of,

when sinking shafts in quicksand, by means of the freezing process, thusenabling the observers to ascertain to what extent the soil has alreadybecome solidly frozen.

.In the place of the seismometer proper, which mechanically indicatesthe shocks produced and records them by the aid of a eliograph, use maylikewise be made of a microphone adapted to render the shocks audible bymeans of an electric current in a telephone or in a alvanometer. This isbased on an appreclation of the fact that, according to the elasticproperties of the subsoil, the pitch of the waves produced by artificialshocks will vary, for instance more nearly resembling a ring than a thudin which case frequently characteristic accessory sounds will inaddition make themselves heard. By comparison with the by directreference to spots the geological structure of which is known, the trueinferences may then be drawn.

To this end, acoustic appliancesknown ,as terrestrial listening devicesand which have been widely employed during the late war for the purposeof determining minmg operations on the part of the enemy, may bedirectly made use off, since devices of this kind are already suitablydesigned or else may be easily adapted to the purpose had in view. Itwill thus be understood that in the place of the pendulum use is made ofa microphone, placed face down on the ground or slightly buried therein,and,.1nstead of a photographic recorder, a telephone or galvanometer orthe llke is em ployed. I may however also record the travelling timecurve by photographically recording the fluctuations of current arlsingwithin the microphone by means of an oscillograph or a like apparatus,the telephone being merely employed for the reception by sound. The useof a microphone further permits of ascertaining the moment at which theartificial concussions take place. By employing a microphone influencedboth by the terrestrial and by the air waves one obtains two marks, onesucceeding the other, in the curve recorded and which allow of easilycomputing the said moment. I may however also employ two separatemicrophones, one for the terrestrial and one for the air sounds andconnect them with the oscillograph or the photographic recorder.

A device of this sort is fully equivalent, as far as accuracy ofmeasurement is concerned, to-the seismographic apparatus, but exceedsthis latter in point of simplicity and light weight. V

The methods hereinbefore described may however also be employed incombination, the acoustic receiver being for intance made use of incarrying out certain preliminary tests furnishing general data as to thegeological character of a region, whereupon more exact specialinvestigations are carried out with the aid of the seismometer.

I claim:

1. The method of ascertaining geological tectonic formations whichcomprises generating artificial seismic waves so as to cause them to betransmitted through the ground from a point selected at will anddetecting the characteristics of "said waves at a determinable distancefrom said point.

2. The method of ascertaining geological tectonic formations comprisinggenerating 'acteristics of said waves and artificial seismic waves so asto cause them to be transmitted through the ground from a point selectedat will, detecting the charfrom said detected characteristicsdetermining subsurface strata.

3. The method of ascertaining geological tially' at the surface oftectonic formations which comprises causing an explosive charge todetonate substanthe earth so as to transmit artifically generatedseismic waves through the ground from a point selectedat will anddetecting the characteristics of I said waves.

4. The method of ascertaining geological tectonic formations whichcomprises generating artificial seismic waves so as to cause them to betransmitted through the ground from a point selected at will andascertaining the travelling speed of said waves by observations atseveral distances from said point.

5. The method of ascertaining geological tectonic formations whichcomprises generating from a point selected at will and substantially atthe surface of the earth artificial seismic waves through the ground andascertaining the travelling speed of said waves so as to cause them tobe transmitted by means of a seismograph set up at a distance from saidpoint.

6. The method of ascertaining geological formations which comprisescausing an explosive charge to detonate at a point substantially at thesurface of the earth so as to transmit seismic waves through the groundand ascertaining the travelling speed of said waves by means of aseismograph set stantially at the surface of the earth so as to transmitseismic waves through the ground and receiving at a measurable distancefrom said point those seismic waves which precede the sound waves due tosaid detonation.

8. The method of ascertaining geological formations which comprisescausing an explosive'charge to detonate so as to transmit seismic wavesthrough the ground from a point selected at will and detecting the charateristics of said seismic waves as well as of the sound waves generatedby said detonation.

9. The method of ascertaining geological formations which comprisescausing an explosive charge to detonate so as to transmit seismic andsound waves through the ground from a point selected at will anddetecting I 1 11. The method of determining subsurface strata whichcomprises generating artificial seismic waves so as to cause them tobetrans: mitted through the ground from a point selected at will andascertainin the travelling speed of said waves invthe ifierentunderstrata which comprises generating artificial 10 seismic waves so asto cause them to be trans ground beds.

12. The method of determining subsurface mitted through the ground froma point selected. at will and ascertaining the travelling speeds of saidwaves in-the different finderground beds by noting the distance betweenthe generating point and the point of observation and by observing therunning time strata which comprises generating artificialthe surface. 1

seismic'w-aves so as to cause them to be transmitted through the groundand observing the travelling speed of "said waves over g'radu of travelmeasured at :0

ated known distances 15. The method of determining subsurface stratawhich comprises causing a plurality oi: explosive charges to detonate soas to transmit artificial seismic waves through the 85 ground frompoints selected atwill at a plurality of; distances from the detectinpoint and ascertaining the travelling spee of said 'waves by recordingthe running times of said waves on .a seismograph .at

detecting point. p 16. The method of determining the depth of subsurfacestrata which comprises causing an explosive charge to detonate so astotransmit artificial seismic Waves through the I ground from a pointselected at will andascertaining the running time and the travellingspeed of said waves by recording on a seismograph. Y

In testimony whereof I afiix my signature.

Dr. .LUDGER MINTROP;

CERTIFlCATE or commoner;

patent N I 599 558 LUDGER MINTROP September 1h, 1926.

'It is hereby certified that error appear-sin the printed specificationof the above numbered patent requiring correction as follows: Page 5',second column, line 87, claim 5, strike out the words "so 'as to causethem to be transmitted -and insert the sanie after "waves" in line 85,same claimrenii that the said Letters Patent should be read with thiscorrection thereinthat the same may confornto the-record of the-case inthe Pa tentiiffice.

Signed and sealedthis 31st day of May, D.- 1938.

(Seal) Henry Van lirsdale, Acting Commissioner of Patents.

